Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 85	$ 75
Interest cost	208	264
Expected return on plan assets	(376)	(393)
Amortization of net loss	188	107
Net periodic cost	$ 105	$ 53